Hello from Adelaide

[bobbycf]

Hey guys

Im from Adelaide and decided to join this firum as my limited knowledge and skills on mower repairs dealing with a tricky problem on an d 3.5hp briggie is becoming very frustrating.

i picked up this old 3.5hp briggie mower with auto choke where it wasnt starting.
Ive been fixing a lot of manual choke with primer ones without any problems but this one has become an impossible puzzle.

it only starts when fuel is manually fed through air i take but dies down immediately.

replaced the diaphragm with a genuine briggie and cleaned the carb and the two plastice tube fuel filters blowing with my mouth and air goes through so should fuel as well.

into the wells under the carby there is fuel meaning its sucking fuel and filling the reservoir from the tank.

the choke is working fine as when you push it down with a screw driver from the top of air filter inlet it releases itself.

yet the mower wont start. There is ignition happening and played the the mixture adjustment screw and no luck.

any experts out there who had the same exact issue and found a fix?

The model number labels are missing so i have no model number. Only a photo. The diaphragm part number was 391681.


much appreciated

 

[bertsmobile1]

Slip the fuel tank off complete with carb
Blow down the air horn with low pressure air
A good way to do this is to put a dunny roll center over the air inlet then blow using an air duster held about 1" or so above the top of the cardboard.
You should see atomised fuel coming out of the outlet side of the carb.
If so there is nothing wrong with the carb and you are looking for a split in the manifold or damaged valves .

 

[bobbycf]

I have just an air comressor but havent tried pressured air in it.

I was thinking if it turns on putting fuel in manually then the cylinder side of the engine and valves should be ok.

Its more like fuel not getting to the manifold at all so has to be a carb problem but unsure what.

so by your advice I will remove tha tank and carb and try blowing air in it and see what happens.

last week i did take the carb out and soaked it in petrol to give it a good clean but that didnt work.

might be a blocked carby maybe?

 

[bertsmobile1]

IF it came through my gate then did what you said the air test is the first thing I do which saves me pulling the carb off the tank and replacing a perfectly good diaphragm & gasket.
I have assumed you fitted them correctly, diaphragm to the tank.
The induction tube ( manifold if you like ) is a thermo setting plastic so will shrink & crack with exposure to sufficient heat .
Also doubt the security of the O ring seal between the carb & induction tube .

 

[Catherine]

Welcome to the forum!

I'm going to move this thread over to our mower and equipment operation section.

 

[bobbycf]

IF it came through my gate then did what you said the air test is the first thing I do which saves me pulling the carb off the tank and replacing a perfectly good diaphragm & gasket.
I have assumed you fitted them correctly, diaphragm to the tank.
The induction tube ( manifold if you like ) is a thermo setting plastic so will shrink & crack with exposure to sufficient heat .
Also doubt the security of the O ring seal between the carb & induction tube .

Well the diaphragm is placed correcty and carefully. The intake manifold on this one is metal but ive seen the plastic ones on ther ones i have fixed before.

i did blow the carb with compressed air yesterday but that didnt fix the issue.

when i add a bit of fuel thru air intake it turns on and dies ss soon as that fuel is burnt off.

i will remove the carb again and check everything but i did noticed after emptying the tank and cleaning the carb and putting it back on there was fuel in the reservoir (or shatever its called) under the carb.

i did also remove the cylinder head snd inspected the valve seals and piston and it appeared to be fine.

took the oil out and refreshed with new oil as the old oil was black as.

im suspecting the carb but its a very simple thing and pitty i cant remove the bloody fuel filter tubes to clean inside the them thoroughly. Very bad design. But shen seeing the fuel under carb would have thought its sucking he fuel therefore its working.

As oppose to the carbs with manual priming button which shoots fuel through to the manifold into the cylinder i cant figure out how these auto choke carbs actually shoot the fuel into the manifold.

there is no where i could see in it where fuel could be sprayed into the manifold.

 

[bobbycf]

Welcome to the forum!

I'm going to move this thread over to our mower and equipment operation section.

Thanks. My appologies if i posted in the wrong section.

 

[bertsmobile1]

Blowing air through the carb is not supposed to fix anything, it is a test to see if the carb is actually atomizing fuel .
As I do it regularly I can tell if the carb flow is restricted or not.
And yes it is a very simple carb.
They are everywhere 2nd hand because of all the old B & S engines which have failed.
I use to keep them but now they go into the plastic recycling .

 

[bobbycf]

did take out the carb and re-installed the diaphragm. Ran air through every in/out of the carb didnt notice any atomized fuel spitting out.

air seems to go through both fuel filter tubes though with extremely low pressure due to the nozzle pin hole in the section where you adjust the fuel/air ratio.

Still not turning on.

took the cylinder head and inspected pistons and cylinder walls no crack and pistons seem to work fine.

on the models with priming button you press to spray fuel into yhe manifold but on these ones that are auto choke/self priming i cant see where and how the fuel gets sprayed into the manifold ghrough to the cylinder.

when i pull the cord although im getting spatks but no sign of fuel at all. Must the carb be still blocked somehow?

 

[bobbycf]

Out of the two fuel filter tubes attached to the carb the longer one that goes into the tank has decent flow when i blow woth mouth through it but doesnt seem to fill the reservoir.
The other one which is supposed to suck fuel and shoot through to intake manifold seems to be hard to blow into.

anyone please? Anyone had the same exact problem and managed to fix it withought having to buy a new carby?